I want to do something like this:

function make_object_from_flag(x, y, flag)
 local flag_obj = {
    [1] = make_impassable_object(x, y),
    [2] = make_coin(x,y),
    [4] = make_screen_transition_object(x, y),
 }

 flag_obj[flag] 
end

But for some reason it keeps saying flag_obj[flag] is a syntax error: syntax error line 119 (tab 0) flag_obj[flag] syntax error near 'end' attempt to call a string value

Oddly enough, if I comment out flag_obj[flag] but leave the flag_obj table uncommented, it says I run out of memory despite only having a few hundred lines of code

here's the entire code snippet if you need more context:

function define_map_objects(mapw, maph)
--Iterates through every sprite on the map and makes it an object specified on its flag
	for i=0,mapw do
		for j = 0,maph do
			local cell = mget(i,j)
			make_object_from_flag(i*8, j*8, fget(cell))
		end
	end
end

function make_object_from_flag(x, y, flag)
	local flag_obj = {
		[1] = make_impassable_object(x, y),
		[2] = make_coin(x,y),
		[4] = make_screen_transition_object(x, y),
	}
	flag_obj[flag]
end

when you do table[key]
it looks for that key and the table doesn't have it.. Like:

t={
 apple="poops",
 jar="nowhere!"
}
print(t[apple]) -- poops
print(t[cup]) -- nil? where is cup?

Also checking it on it's ownsome; the compiler won't like that.

So ya not sure what your trying to do, if your running out of memory it probably means it's calling it's self.

@picodrake your factory function is a good start but you are mixing function reference and function call.
when writing:

...
[2]=make_coin(x,y),
..

the code is actually invoking make_coin function and stores a coin at table index 2.
this is why you end up with a out of memory error.
the code created maph x mapw x 3 ‘objects’!

the fix is to reference the functions in the table and delay the call, eg:

function make_thing(x,y,flag)
 local factory={
...
— register a function reference 
[2]=make_coin,
...
}
— call function with current parameters 
factory[flag](x,y)
end

@freds72 thank you so much! That was a great explanation and it makes a lot of sense. For some reason its still throwing up errors, but when I replicated it in a blank program it worked just fine, so I'm assuming it's just some syntax issue I can weasel out.